MODAL DECOMPOSITION OF NON-LINEAR INTERACTIONS IN WALL TURBULENCE

Abstract

© 2022 12th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2022. All rights reserved.Coherent structures are found in many different turbulent flows, and they are known to drive self-sustaining processes in minimal-unit turbulence. Identifying the triadic interactions between coherent structures can provide insights beyond what is possible in the framework of linearised models. There are infinite possible interactions that may generate a given structure, and thus a method to systematically study those, ranking them in terms of their contribution, is of interest. We here use the resolvent-based extended spectral proper orthogonal decomposition (RESPOD) approach (Karban, U. et al. 2022 Self-similar mechanisms in wall turbulence studied using resolvent analysis. Journal of Fluid Mechanics 969, A36) to identify the relevant triadic interactions for a minimal Couette flow at Reτ = 34, studying the interactions that give rise to wall-attached structures, obtained by measuring the wall-shear. Our analysis reveals that there are six triadic interactions that dominate the most-energetic wall-attached structure.